Issue 38

T. Morishita et alii, Frattura ed Integrità Strutturale, 38 (2016) 281-288; DOI: 10.3221/IGF-ESIS.38.38 284 0.5 1.0 0.5 1.0 Failure life N f , cycles Strain range Δε eq FF SS SS* Push-pull Circle 10 4 10 3 10 1 10 2 Figure 3 : Comparison of creep-fatigue failure lives. 10 2 10 3 10 4 Factor of 2 PP-FF PP-SS PP-SS* PP-TH-3 PP-TH-10 PP-CH-3 PP-CH-10 1.0 2.0 Mises' equivalent strain range  eq , % Failure life N f , cycles CI-FF CI-SS CI-SS* CI-TH-3 CI-TH-10 0.4 0.2 Figure 4 : Correlation of N f by Mises’ equivalent strain range. In multiaxial low cycle fatigue tests, it has been reported that the large reduction in the failure life has a close relation with strain path and material. Itoh et al. [8-13] proposed a non-proportional strain range  NP for life evaluation under non- proportional loading defined by   I NP NP Δε α1 Δε f  (2) where  I is a maximum principal strain range under non-proportional loading which can be calculated by  and  .  and f NP are a material constant and a non-proportional factor, respectively. The former is the parameter related to the additional hardening due to non-proportional loading and the latter is the parameter expressing the intensity of non- proportional loading. The value of  is the ratio to fit the failure life in the CI test to that in the PP test at the same  I . f NP is defined by [12]